1. Field of the Invention
This invention generally relates a laser measurement system for determining the location of active targets in three-dimensional space, and more particularly to a laser measurement system for determining deformation in vehicle bodies for automobile collision repair using a laser scanning apparatus in conjunction with a plurality of active targets suspended from known reference points on the vehicle to calculate three dimensional spatial coordinates defining the actual positions of the active targets which is then compared with manufacturer-provided specification values to determine the extent of deformation of the vehicle body.
2. Background of the Invention
Vehicle frame deformation measurement systems, such as disclosed by U.S. Pat. Nos. 4,997,283, 5,251,013 and 5,801,834, use a pair of rotating laser light beams emitted from a laser measuring unit, however, these measurement systems scan passive reflective targets that have strips of reflective and non-reflective material to create a pulsed beam of reflected laser light. In these known systems, the pulses of reflected laser light from the passive targets are sensed and counted by the laser measuring unit. The resulting count is then used by a computer to calculate the position of the targets, compare it to a reference data base and then calculate the deformation of the vehicle frame. More particularly, the laser measuring unit comprises a helium-neon laser that emits a laser beam which is split into two laser beams by a 50/50 beam splitter, each beam then being directed to a rotating mirror. The rotating mirrors direct the laser beams in a 360 degree circle, with both beams being directed in a single plane. The beams sweep across the surfaces of the reflective targets attached to the reference holes on the vehicle.
In the Inventions of the above-noted patents, the reflective targets are passive devices that do not detect the laser light nor do they interact electronically with the laser measuring unit, but rather merely reflect the laser light signal. Each coded target contains strips of reflective and non-reflective material, the reflective strips reflecting the scanning laser beam back to its source as a series of pulses of light. These reflected pulses are registered as “on” events (or counts) by the electronics on board the laser measuring unit. A counter counts the number of counts (as measured by an oscillator) from zero to the edge of each reflective, non-reflective border.
A computer receives the count information for each target and computes the angle from the center of each mirror to the center of each target. With the two angle measurements (one for each mirror and target), and the known baseline between the two mirrors, the planar (X,Y) coordinates of each reference hole are computed using trigonometry. The third coordinate (Z coordinate) is calculated using Z coordinate-representative sizing of the reflective and non-reflective stripes on the coded targets.
The scanning arrangement used in the above arrangement is complicated, requiring the use of rotating mirrors to create two laser beam sources each rotating around their respective points of origin. In addition, the targets themselves do provide indications to the repair technician indicating which way and how far a particular target is out of alignment as compared to the reference points.